.\" Copyright 2016, IBM Corporation.
.\" Written by Mike Rapoport <rppt@linux.vnet.ibm.com>
.\" Copyright 2016, Michael Kerrisk <mtk.manpages@gmail.com>
.\" Copyright 2024, Alejandro Colomar <alx@kernel.org>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH UFFDIO_ZEROPAGE 2const 2024-06-17 "Linux man-pages 6.9.1"
.SH NAME
UFFDIO_ZEROPAGE
\-
zero out a memory range registered with userfaultfd
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.BR "#include <linux/userfaultfd.h>" "  /* Definition of " UFFD* " constants */"
.B #include <sys/ioctl.h>
.P
.BI "int ioctl(int " fd ", UFFDIO_ZEROPAGE, struct uffdio_zeropage *" argp );
.P
.B #include <linux/userfaultfd.h>
.P
.fi
.EX
.B struct uffdio_zeropage {
.B "    struct uffdio_range  range;"
.BR "    __u64                mode;" "      /* Flags controlling behavior */"
.BR "    __s64                zeropage;" "  /* Number of bytes zeroed */"
.B };
.EE
.SH DESCRIPTION
Zero out a memory range registered with userfaultfd.
.P
The following value may be bitwise ORed in
.I mode
to change the behavior of the
.B UFFDIO_ZEROPAGE
operation:
.TP
.B UFFDIO_ZEROPAGE_MODE_DONTWAKE
Do not wake up the thread that waits for page-fault resolution.
.P
The
.I zeropage
field is used by the kernel to return the number of bytes
that was actually zeroed,
or an error in the same manner as
.BR UFFDIO_COPY .
.\" FIXME Why is the 'zeropage' field used to return error values?
.\" This should be explained in the manual page.
If the value returned in the
.I zeropage
field doesn't match the value that was specified in
.IR range.len ,
the operation fails with the error
.BR EAGAIN .
The
.I zeropage
field is output-only;
it is not read by the
.B UFFDIO_ZEROPAGE
operation.
.SH RETURN VALUE
This
.BR ioctl (2)
operation returns 0 on success.
In this case, the entire area was zeroed.
On error, \-1 is returned and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EAGAIN
The number of bytes zeroed (i.e., the value returned in the
.I zeropage
field)
does not equal the value that was specified in the
.I range.len
field.
.TP
.B EINVAL
Either
.I range.start
or
.I range.len
was not a multiple of the system page size; or
.I range.len
was zero; or the range specified was invalid.
.TP
.B EINVAL
An invalid bit was specified in the
.I mode
field.
.TP
.BR ESRCH " (since Linux 4.13)"
The faulting process has exited at the time of a
.B UFFDIO_ZEROPAGE
operation.
.SH STANDARDS
Linux.
.SH HISTORY
Linux 4.3.
.SH EXAMPLES
See
.BR userfaultfd (2).
.SH SEE ALSO
.BR ioctl (2),
.BR ioctl_userfaultfd (2),
.BR userfaultfd (2)
.P
.I linux.git/\:Documentation/\:admin\-guide/\:mm/\:userfaultfd.rst
